OK, that helps. Let me explain fully what I am thinking/trying to do (thread drift but on topic, may benefit OP as well as me).
1) have my 20” NM gun figured out, you and others helped me with that earlier this winter. 1-4 glass for it. Great help I already received.
2) this is in regards to a 16” gun - I found an early gen1 S&W upper at a great price recently. The very early ones with the Thompson Center barrels, 4150, 1/8, 5R rifling, government profile. Not a match barrel, but they are quite good; very good - I’ve had them before. My thinking was to put on a ff handguard and mate it to a spare complete lower I have in the safe, put in a RR trigger.
When I bought my RR barrel for the 20” NM gun, I had them send me a .050” front post (part, not installed). I was thinking that I could put that into the 16” upper, with a carry handle but would need to get a small aperture for it. I have a spare S&W carry handle for that purpose if I want to go that way, standard .840 6/3 for carbine. I could just change that rear aperture vs. putting glass on it is what I was thinking. This is mostly summer shooting in PNW, so clear and sunny (but definitely not so at other times).
My thinking is based on past experience with skiing, sailing, horseback riding, motorcycling etc. The more you used other equipment, the more you learned about how much equipment was a factor, how much was “you,” and it made you more skilled - independent of the equipment. (If that makes sense). So I would shoot both guns at 200, 300 yds but also, I would like to have an extra gun that can shoot adequately to 200 yards in case my step-son and I go to a match and the squadding does not allow us to use the same 20” gun. I think that is very likely at local matches.
My dad was a machinist in a prior life, and has a well-equipped garage/shop so I can do my own work (and I have a lot of experience, not just winging it); I have pilot bits and could drill out an aperture. I am just wondering if my plan is sound (or I should just put glass on it - the 2nd carbine). I know it’s a little bit of thread drift (see what I did there?), but it’s close enough I figure OP does not mind. ;)
Long-winded explanation but I figure better to get it out now and get advice from the Pros from Dover as much as possible vs. learning the harder way on my own this spring and summer.